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SQUARE WAVE TIG 255
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F-29
TROUBLESHOOTING & REPAIR
ACTIVE SCR TEST
(continued)
PROTECTION/SNUBBER
L9255
J10
J11
J12 J13
J14
J15
REMOVE PLUGS J10 & J13
TEST PROCEDURE
1. Remove main supply power to machine
2. Remove plugs J10 and J13 from protec-
tion/snubber board. See Figure F.13.
3. Remove red insulating paint from heat
sink test points. See Figure F.14. DO
NOT DISASSEMBLE THE HEAT
SINKS.
FIGURE F.13 - PROTECTION/SNUBBER BOARD PLUG LOCATIONS.
SCR1
ANODE
CATHODE
(1 & 2)
SCR2
ANODE
SCR3
CATHODE
SCR4
CATHODE
ANODE
(3 & 4)
PLUG
P10
FIGURE F.14 - SCR TEST POINTS.
4. Perform test procedure as outlined in
Figure F.15. Repeat test for all four
SCR’s
5. Replace any SCR assembly that does
not pass test in Step 4